This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-089327, filed Mar. 30, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a display apparatus capable of improving picture quality at the time of displaying MPEG-4 pictures.
The present invention relates to a system for adaptively switching a drive method according to a specific position on a display panel and to a display apparatus optimal to display MPEG-4 pictures.
An active matrix type display apparatus, i.e., a liquid crystal display (LCD) apparatus stands an important position as a key device for a personal computer or a television monitor. It is also expected that the active matrix type display apparatus will become increasingly significant in the future display field due to its characteristic space saving, power saving and light weight.
Initially, the LCD apparatus was faced with various problems to be cleared up as a color display. Thanks to technological innovation and devoted exertions, these problems have been solved gradually one by one. Nevertheless, there is still a demand for further enhancing the performance of the LCD apparatus.
Approaches to further improve the LCD apparatus span several technical fields. One is an approach to deal with the afterimage phenomenon of the LCD apparatus. The other approach is to satisfy the requirements of technological innovation to follow up the trend of new technology in video media systems.
The video media systems include, for example, an MPEG (Motion Picture Experts Group) system targeting at digital broadcasting, DVD and the like. An MPEG-4 (Motion Picture Experts Group Phase 4) system has, in particular, successfully realized an LCD apparatus which saves power and reduces cost.
Now, the MPEG system will be described. First, the conventional case relating to the afterimage correction of the LCD and the reduction of the number of display bits will be described. Thereafter, a video picture encoding method, to which the present invention is applied as will be described later, will be outlined, while taking an MPEG-4 (Motion Picture Experts Group Phase 4) system which is one of the international standards for video picture encoding as an example.
First, the conventional technique relating to the afterimage correction will be described.
In a liquid crystal display (LCD) apparatus, when a state in which an electric field is applied to the liquid crystal is changed to a state in which an electric field is not applied thereto or when a state in which an electric field is not applied to the liquid crystal is changed to a state in which an electric field is applied thereto, the orientation direction of liquid crystal molecules changes. However, because of the response characteristics of the liquid crystal molecules, i.e., the characteristic of the rise or fall of change thereof, a state exhibiting desired optical characteristic cannot be sometimes obtained. This is visually recognized as an afterimage, which may possibly cause the deterioration of picture quality.
It is, therefore, necessary to cancel this afterimage phenomenon. To do so, there are proposed configurations in which an LCD apparatus is provided with an additional section to cancel the afterimage phenomenon. Those configurations include, for example, that shown in a technique disclosed by Japanese Patent Unexamined Application Publication No. 3-98086. The problem with the provision of this additional section is, however, to disadvantageously enlarge overall circuit size.
In a conventional LCD apparatus, if a video picture is displayed, pixel display contents are rewritten in units of pixels on the picture plane of a frame or a field according to picture signals supplied in units of frames or fields, thereby displaying the video picture on the image plane. That is, irrespectively of whether or not there is a change in the pictures between frames or fields, picture signals are re-input to all pixels. Owing to this, a write operation never fails to be carried out even to the pixels which do not have any picture change and do not need to be written.
In case of, for example, a configuration of 400xc3x97480 dots (=192,000 dots), since color display requires three types of colors R (red), G (green) an B (blue), the number of pixels constituting a picture plane amounts to 192,000xc3x973 (R, G and B)=576,000 dots. In case of a configuration of 600xc3x97800 dots (=480,000 dots), the number of pixels constituting a picture plane amounts to 480,000xc3x973 (R, G and B)=1,440,000 dots. Since the LCD comprises two or three driving transistors for each dot of R, G and B, the 576,000-dot configuration is required to drive at least 1,150,000 transistors, and the 1,440,000-dot configuration is required to drive at least 2,880,000 transistors.
Considering that such a huge number of transistors are driven once per frame (30 frames per second in case of the television system), power consumption for each write operation may be substantial.
Meanwhile, if video pictures adopt the MPEG-4 encoding system, it is possible to provide a background region and an object region separately. Namely, in that case, it is not necessary to rewrite all of the pixels on a frame. If rewriting only the picture in a change region by using address information on the change region and difference information on the picture, the video pictures can be displayed.
While paying attention to this fact, if an LCD reconstructed picture is one according to the MPEG-4 video compression encoding system, the LCD apparatus is scanned not by a television scanning method for rewriting all the pixels of a frame but by a driving method which can rewrite only the pixels in the change region on a frame. With use of this driving method, the picture signal transfer amount of the MPEG-4 video picture compression method can be reduced. Further, even for the LCD apparatus, it is possible to pave the way for the lower power consumption of the LCD by utilizing the picture signal transfer amount reduction effect.
The MPEG-4 is, in particular, aimed to be utilized for the transmission of video pictures by employing an existing communication line having not so fast transmission rate, multimedia communication by means of mobile computer terminals or the like, videophones and the like. In case of a mobile terminal (portable terminal), in particular, power supply relies on batteries. Thus, it is and it will be a very significant challenge to save the power of the LCD apparatus which has a large effect on power saving among the constituent elements of the portable terminal.
It is, therefore, an object of the present invention to provide a display apparatus capable of reducing LCD driving power without deteriorating display quality at the time of displaying encoded video data.
According to the invention, there is provided an active matrix type display apparatus comprising: an active matrix type display panel having a plurality of pixels arranged in a matrix, signals lines for inputting a video signal to the plurality of pixels, and switching elements configured to select the plurality of pixels individually; a video decoder configured to decode an input compressed video data, and obtain a reconstructed picture signal for each picture; a change region detector configured to detect a change region between a previous picture and a current picture by using the reconstructed picture signal obtained by the video decoder, and obtain address data on the change region; a display signal converter configured to input the reconstructed picture signal, and convert the reconstructed picture signal into a display picture signal; a difference signal detector configured to input a display picture signal of the previous picture and a display picture of the current picture, and detect a difference signal indicating at least a difference between the previous picture and the current picture; a switch driver configured to selectively drive the switching elements and select the pixels corresponding to the change region in accordance with the address data obtained by the change region detector; and a signal line driver configured to add the difference signal obtained by the difference signal detector and the display picture signal of the previous picture, and input an addition result to the signal lines.
According to the invention, there is provided an active matrix type display apparatus comprising: an active matrix type display panel having a plurality of pixels arranged in a matrix, signals lines for inputting a video signal to the plurality of pixels, and switching elements configured to select the plurality of pixels individually; a video decoder configured to decode an input compressed video data and obtain a reconstructed picture signal for each picture; a change region detector configured to detect a change region between a previous picture and a current picture by using the reconstructed picture signal obtained by the video decoder, and obtain address data on the change region; a display signal converter configured to input a reconstructed picture signal of the previous picture and a reconstructed picture signal of the current picture signal, and convert the reconstructed picture signals into display pixel signals having different amounts of display data between the pixels belonging to the change region and the pixels which do not belong to the change region, respectively; a difference signal detector configured to input a display picture signal of the previous picture and a display picture of the current picture, and detect a difference signal indicating at least a difference between the previous picture and the current picture; a switch driver configured to selectively drive the switching elements and select the pixels corresponding to the change region in accordance with the address data obtained by the change region detector; and a signal line driver configured to add the difference signal obtained by the difference signal detector and the display picture signal of the previous picture, and input an addition result to the signal lines.
According to the invention, there is provided a liquid crystal display apparatus comprising: a liquid crystal panel having a plurality of pixels arranged in a matrix, signals lines for inputting a video signal to the plurality of pixels, and switching elements configured to select the plurality of pixels individually; a video decoder configured to decode an input compressed video data and obtain a reconstructed picture signal for each frame; a change region detector configured to detect a change region between a previous frame and a current frame by using the reconstructed picture signal obtained by the video decoder, and obtain address data on the change region; a display signal converter configured to input a reconstructed picture signal of the previous frame and a reconstructed picture signal of the current frame, and convert the reconstructed picture signals into display picture signals, respectively; a switch driver configured to selectively drive the switching elements in accordance with an address signal obtained by the change region detector; and a signal line driver configured to add the difference signal obtained by the difference signal detector and the display picture signal of the previous frame, obtain a display picture signal having display bits for the pixels belonging to the change region of the current frame set fewer than display bits for the pixels belonging to other regions, and input the display picture signal to the signal lines.
With this configuration, a video signal corresponding to a region having a difference between the reconstructed picture signal of the previous frame and that of the current frame is supplied to the crystal display panel. As a result, the picture is displayed on the crystal display panel by rewriting only the picture in the difference region or the picture in the difference region is displayed by lowering the resolution.
Therefore, the picture is rewritten only for the change region, thereby making it possible to rewrite the change region in a one-frame time and to provide a display apparatus capable of reducing LCD driving power without deteriorating display quality.
Attention is particularly paid to rewriting a picture. In a conventional liquid crystal display apparatus, irrespectively of whether or not there is a change in the pictures between frames or fields, picture signals are re-input for all pixels. Owing to this, power consumption is increased by a write operation for the pixels which do not have any picture change and do not need to be written. According to the present invention, write operation is carried out for the pixels of the changed region and not for those of the unchanged region, whereby power consumption can be reduced.
According to the present invention, the number of display bits for pixels or groups of a plurality of pixels belonging to the change region of the current frame is set lower than that of display bits for the pixels or groups of a plurality of pixels which do not belong the change region.
As for the change region or particularly the continuously change region of a picture, it is difficult for human eyes to perceive the resolution of the region due to the human biological properties. Utilizing this, the picture in a moving region is displayed with fewer display bits to lower the resolution. If the number of display bits is decreased, time required for data transmission can be shortened accordingly. Besides, the picture is rewritten only for the change region. Thus, it is possible to rewrite the picture for the change region within a one-frame time and there is less fear of deteriorating apparent display quality. Further, if the resolution is lowered (i.e., the number of display bits is decreased), the driving power of the driver can be reduced, whereby picture quality can be maintained and a display apparatus capable of reducing LCD driving power.
In a conventional display apparatus, irrespectively of whether or not there is a change in the pictures between frames or fields, picture signals are re-input for all pixels. Owing to this, power consumption is increased by a write operation for the pixels which do not have any picture change and do not need to be written. According to the present invention, write operation is carried out in units of pixels, whereby power consumption can be reduced.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.